There are multiple methods of measuring arterial blood pressure using an inflated cuff on the arm or other appendage. The most common manual method used is the auscultation method. In this method, the clinician inflates a cuff around the arm to a pressure well above the expected arterial blood pressure. He or she then slowly deflates the cuff while listening with a stethoscope for sounds made by the return of blood flow in the artery. The pressure in the cuff corresponding to the first sounds in the artery corresponds to the systolic blood pressure and the pressure in the cuff corresponding to the departure of sounds from the artery is the diastolic blood pressure. While this method works well for manual measurement, it is impractical for automated noninvasive blood pressure measurement.
Automated blood pressure measurement devices use the oscillometric method of blood pressure measurement. In this method, the blood pressure cuff is inflated and is deflated in pressure steps. At each pressure level, an electronic pressure sensor evaluates the relative amplitude of the pulses created by the artery under the cuff at that specific pressure level. By evaluating the relative pulse amplitude over a range of cuff pressure levels from well above the expected systolic pressure to well below the expected diastolic pressure, the automated monitor builds an array of pulse amplitudes. The system then evaluates the measured pulse amplitudes to calculate the systolic, diastolic and mean blood pressure values. The pressure where the maximum pulse amplitude is observed (Am) is the mean blood pressure. The cuff pressure above the mean where the pulse amplitude is 50% of the maximum observed amplitude is taken as the systolic blood pressure (As) and the cuff pressure below the mean blood pressure where the pulse amplitude is 75% of the maximum observed pulse size is generally taken as the diastolic blood pressure (Ad), as shown in FIG. 1.
The oscillometric method assumes that the size of the measured pulses, or throbbing, is related to the blood pressure and that the maximum throbbing occurs when the cuff pressure matches the mean arterial pressure of the blood in the arteries under the cuff. Because this oscillometric blood pressure measurement method is easily automated it is built into many patient monitoring systems.
Clinicians commonly train for procedures such as taking a patient's blood pressure using the oscillometric method using a simulation. Most blood pressure simulation systems use actuators to drive a piston to create simulated blood pressure pulses within the tubing connecting the blood pressure cuff to the monitor, rather than impinging the blood pressure cuff directly. Since these systems do not control the volume of the cuff, they are limited in the range of blood pressures they can simulate and the accuracy of the simulation. Depending on the volume of the cuff inflation these actuator systems may not be able to create the simulated arterial pulses needed to generate the correct simulated blood pressure values.
Thus, clinicians are not able to practice using a simulation that accurately trains on the fully range of blood pressure values that the clinician may see in clinical practice.
Consequently, there is a long felt need for a technology that could more accurately simulate the clinical experience of using oscillometric blood pressure measurement across a broad range of values.